Which 35mm SLR camera had the first pentaprism? Was it the Rectaflex or the Contax S? This question has turned into a bit of a conundrum over the years – many sources cite the Contax S as the first, with just as many opting for the Rectaflex. This discussion tries to provide some insight into the timeline of pentaprism use by looking at both the patents for cameras containing pentaprisms, and the cameras actually produced. Note that some original historical patents are hard to find, e.g. those from Italy.

In all probability the idea of using a pentaprism in a camera had been floating around for a while. On 28 January 1933, German architect Kurt Staudinger was issued a patent for a reflex device with eye level vision, which used a pentaprism-like system (DE556783A, “Vorrichtung fuer Reflexkameras” (Device for reflex cameras). The invention related to a device which “…is intended to convert the horizontal and reversed image projected into the screen into a vertical, upright and reversed image.” However instead of using a prism, this was actually a series of mirrors, i.e. a penta-mirror. Although he tried to interest German camera makers, none were seemingly that eager. At the time there was likely was too much invested in rangefinder cameras to think that an alternative was worthwhile. The only German patent to cite this work was that of Arno Rothe (DE741844A, sub. May 5, 1939) who proposed a reflex camera using mirrors which allowed for both waist level, and eye-level viewing.

From about 1937 Zeiss Ikon began work on a 35mm reflex camera with a pentaprism eye-level viewfinder in the Camera Development Department. The camera was named the Syntax, and on September 2, 1940 Zeiss Ikon applied for a utility patent in Germany. Research has failed to find the German patent, but two patents associated with the camera were filed in France: FR884054 (sub. August 9, 1941) “Photographic apparatus constructed in particular in the form of a monocular mirror reflex camera”, and FR875596 (sub. August 9, 1941) “Mirror camera with photoelectric exposure meter forming part of the camera”. Both applications cite the filing of associated German utility patents on August 23, 1940. There is another Swiss patent submitted by Zeiss Ikon on 18 January 1943 (CH241034) – “Spiegelprisma mit konstanter Ablenkung” or “Mirror prism with constant deflection”. This gives further credence to the fact that Zeiss Ikon was working on a pentaprism for a camera.

Work was slow, but it has been suggested that there was a working model by 1944, supposedly a Contax II body with its metal vertical focal-plane shutter, however having its view/rangefinder replaced by a reflex mirror, delivering an upright and right-way-round image via a roof pentaprism to the eyepiece [1]. However the viewfinder image was too dark, and required f/2 and faster lenses. A diagram of the Syntax from the French patent is shown in Figure 2. According to Siegfried Böhm, design engineer with Zeiss Ikon, there were a series of issues with the Syntax [1]. The camera was complex, and would have required 750 parts to produce, in part due to the vertical shutter, and external bayonet lens mount of the Contax II. Böhm was working on the design for a horizontal focal-plane shutter, however on February 13, 1945, everything related to the project was destroyed by Allied air raids.

The first SLR manufactured with a pentaprism was the Rectaflex. It was the brainchild of Italian lawyer and camera enthusiast Telemaco Corsi (1899-1974), and was the only Italian SLR ever produced. Work began in 1946, and a prototype was shown at the Milan Fair in 1947 (this model used a mirror system instead of a prism). This system seems to be described in a Swiss patent issued in 1949 (CH264025 based on an Italian patent filed in 1947). At the same fair a year later, a working prototype called the Standard 947 was introduced, with the production model A.1000 for sale in September 1948. Only 1150-odd copies were produced, with Rectaflex introducing the B.2000 in April of 1949, and the B.3000 in September. A patent for this pentaprism system is also described in a Swiss patent issued 1954 (CH298155, filed Jul.5/1951) – “Complementary sighting device in a photographic camera equipped with a reflector mirror viewfinder.”, and a West German patent (DE938764) filed the same month.

The Wrayflex was England’s only attempt at developing a 35mm SLR. On Sept. 2, 1952 Wray (Cameras) Limited received a patent for “Reflex Camera with Curtain Shutter” (US2,608.921, filed on 21 May 1948). It matched a UK patent applied for on May 21, 1947 (GB2608921X), describing an SLR which contains a “pentagonal prism”, which appeared at the bottom of the camera, basically upside-down. However this “prototype” never seems to have been put into production.

Instead the Wrayflex production model used a mirror which folds backwards and upwards when the shutter is released. This means there was no space for installing a roof prism – instead the Wrayflex used two mirrors, arranged so as to reflect the ground-glass image twice – this arrangement provides an image which is laterally reversed, but the right way up. The two mirrors must be accurately positioned so that there is no possibility of misalignment. The Wrayflex I and Ia both used mirrors, it wasn’t until the Wrayflex II in 1959 that a pentaprism was incorporated. In addition to the Wrayflex, there is also a patents by Belgian Jean de Wouters d’Oplinter (1905-1973), applied for in Belgium on February 11, and May 29, 1941. The French version of the patent, “Improvements to photographic cameras and similar devices”, was issued on November 10, 1942 (FR879245), however this camera was never produced.

In September 1949, Rectaflex was to received some competition in the form of the Contax S from VEB Zeiss Ikon. The development of the Contax S (also known as the Spiegel-Contax) basically involved recycling the wartime Syntax project. The camera was introduced in 1949. The prism on the Contax S was built into the camera body. The view was life-sized, a result of three factors: the focal length of the lens, the prism itself, and the small magnifying eyepiece behind the prism. Many early prisms were bright in the centre, but susceptible to fall-off in the corners. Later SLRs used systems to overcome this problem – e.g. condensing lenses underneath the ground glass, a flat fresnel lens which spreads out the light, and increases brightness in the corners. While there were a number of patents filed for this camera, most had to do with the shutter mechanism, and shutter release [2]. There don’t seem to be any patents that relate specifically to the pentaprism mechanism (there are war-era patents but that’s another story). Zeiss Ikon certainly marketed their camera in the light that this was the most significant advance since the SLR itself.

Here is the camera being hailed as the most significant advance in camera design since the first miniature itself. The twin-image, coupled range-finder has given way to a single viewer, the Prisma-Scope which enables you to sight directly through the camera lens. You see a life-size image, always upright and non-reversed, that spins into sharp focus with a twist of the lens barrel. For the first time in a single lens reflex, all focusing and viewing takes place at direct eye level. Without sacrificing the compact qualities of the miniature, the nuisance of parallax is forever eliminated … accessory lenses require no coupling with special and costly range-finders … close-up photography requires only the addition of extension tubes. Here is the most versatile camera ever created!

The third pentaprism 35mm SLR was by Swiss company ALPA. However they went in another direction, choosing a prism derived from an Abbe prism, the Kern prism. The main difference between this and a pentaprism prism is the fact that the latter provides a 90° image, while the former is only 45°. So the early ALPA-Prisma Reflex cameras (introduced in 1949) offered an oblique view, not a perpendicular view. This feature continued until the Model 6c of 1960.

What about the Ihagee Exakta? Well the company that basically created the 35mm SLR was slower to adopt the pentaprism. It was not until 1949 that they incorporated the use of an auxiliary prism, the “Prismenaufsatz”, which provided a corrected right to left image (however it did make the camera top-heavy). Finally in 1950 Ihagee, introduced the Exakta Varex. As ALPA’s system did not produce an eye-level image, this really makes the Varex the third camera with an eye-level pentaprism. It was also the first SLR with an interchangeable viewfinder, as the waist-level viewfinder was still the most common of the period. The first Japanese pentaprism SLR did not appear until the Miranda T in 1955, followed by the Asahi Pentax, Minolta SR-2, Zunow, Nikon F and the Yashica Pentamatic.

So who was first? From a practical viewpoint of a manufactured camera, it was the Rectaflex. But I guess it depends on how you interpret history.

Further reading

1. Schulz, A., “From Syntax to Praktina”, Zeiss Historica, 30(1) pp.7-16 (2008)
2. Contax S und Pentacon – History, patents, and design issues with the Spiegel-Contax